Many significant and commercially important uses of modern computer technology relate to images. These include image processing, image analysis and computer vision applications. A challenge in the utilization of computers to accurately and correctly perform operations relating to images is the inability of a computer to correctly distinguish between a shadow and a material object edge within an image, such as a feature of a face depicted in the image, and obscured by an overlying shadow. Thus, for example, many known computer face recognition programs require highly controlled illumination conditions for accurate performance. For correct face recognition under uncontrolled illumination conditions, a computer must be able to identify structures and features of a face that can be modified in appearance due to overlying shadows.
Cognitive processing of the human brain makes it possible for humans to automatically distinguish shadow from object. However, to a computer, the image is all pixel values of varying color characteristics. Accordingly, there is a persistent need for the development of accurate and correct techniques that can be utilized in the operations of computers relating to images, to provide an image appearance optimized for further processing. For example, in computer vision applications such as object recognition, face recognition and optical character recognition, it has been found that a separation of illumination and material aspects of an image into corresponding intrinsic images can significantly improve the accuracy of computer performance.